It has now been established that, because of its high coefficient of action on ozone, trifluorobromomethane (Halon 1301) will have to be replaced, in the shorter or longer term, by refrigerant fluids containing neither chlorine nor bromine and, consequently, having no effect on stratospheric ozone.
Bearing in mind its very low action on the environment, 1,1,1-trifluoroethane (HFA 143a) has already been proposed as a substitute for the CFCs. However, because of its boiling point (-47.6.degree. C.), the use of HFA 143a by itself is restricted to applications with evaporation temperatures near -45.degree. C. and cannot be envisaged for applications with very low boiling temperatures (for example -60.degree. C. to -50.degree. C.).
In fact, the minimum temperature reached in the evaporator is in practice limited by the value of the normal boiling temperature of the refrigerant fluid in order to avoid the entry of air or of brine into the plant in the case of evaporator leakages, which would present the risk of interfering with the normal operation of the system.